Dual-Curing Dental Compositions with High Stability

ABSTRACT

Two-part dual-curing dental compositions containing a hydroperoxide, a thiourea derivative and an acetylacetonate salt as redox radical initiator system, are provided. The dental compositions may contain an acidic monomer for use as a self-adhesive cement. The dental compositions possess enhanced shelf-life stability for working/setting time, bonding strength, color stability, slump, flexural strength/modulus, and when kept at 50° C. for more than 16 weeks.

This application is a continuation of, and claims the benefit of andpriority to, U.S. patent application Ser. No. 16/285,708, filed Feb. 26,2019, which application is incorporated herein by reference.

BACKGROUND

Curable polymer compositions are known for use in dental applications,such as for use in resin composites, cements, adhesives and impressionmaterials. Bonding an indirect dental restoration, such as an inlay,onlay, or crown, to a dental surface usually involves employing dentalcements, which may be self-adhesive or which require a separate adhesivesystem. Self-adhesive compositions provide bonding between a dentalrestoration and a dental structure without pretreating the dentalstructure surface with a primer or bonding agent. Self-adhesive cementscontaining acidic monomers may be preferentially used over traditionalresin-modified glass ionomers or conventional luting resin cements. Theaddition of acid functional monomers makes dental cement compositionsself-etching and self-adhesive, as good bonding may be achieved withoutseparately etching and priming dental surfaces, resulting in lesstechnique sensitivity and lower post-operative sensitivity.

Where self-adhesive cements contain acidic compounds, well-establishedredox initiator used for self-curing, such as benzoyl peroxide and anaromatic tertiary amine, may not function well in the acidicenvironment. If amines are protonated, they may lose potency as areducing agent. Moreover, low thermal stability of benzoyl peroxides mayrequire refrigeration to prevent premature polymerization of thecompositions.

Other redox initiators for use in dental cement compositions are known.U.S. Pat. No. 7,275,932, discloses cumene hydroperoxide andacetylthiourea (CHP/ATU) redox initiator that initiate curing ofendodontic sealing compositions and have improved shelf-life stability,and have acidic compounds that could fasten curing. U.S. Pat. No.7,166,651, discloses self-adhesive dental compositions having cumenehydroperoxide and 1-(2-pydridyl)-thiourea (CHP/PTU) redox initiatorincorporated with an acidic compound for etching, priming and cementing.

U.S. Pat. No. 8,198,343, discloses cumene hydroperoxide andbenzoylthiourea (CHP/BTU) redox initiator as a self-curing initiatorsystem with acidic monomers for self-adhesive cements. U.S. Pat. No.9,889,070, discloses 1,1,3,3-tetramethylbutyl hydroperoxide (THP) and asubstituted cyclic thiourea selected from 4-methyl-2-imidazolidinethione(METU), 4,4-dimethyl-2-imidazolidinethione (DMETU),4-ethyl-2-imidazolidinethione (EETU), or4,4-diethyl-2-imidazolidinethione (DEETU) as redox initiator, withvanadyl acetylacetonate (VO(AcAc)₂) or copper (II) acetylacetonate(Cu(AcAc)₂) to initiate the compositions.

SUMMARY

Two-part, self-curing dental compositions are provided for use in dentalapplications, such as dental provisional materials, resin composites anddental cements. Two-part systems disclosed herein, may also bedual-curing dental compositions, and include compositions that aresuitable for dental cements, including self-adhesive cements andconventional resin cements that require a separate adhesive system.

A two-part dental composition is provided that has a first partcomprising a polymerizable monomer and a hydroperoxide compound as anoxidizing agent. A second part comprises a polymerizable monomer, athiourea derivative as a reducing agent that comprises fluoro ortrifluoromethyl substituted phenylthiourea, which as used herein, refersto a thiourea derivative that comprises phenyl, wherein phenyl comprisesone or more substituents selected from fluorine and trifluoromethyl, andan acetylacetonate salt. The thiourea derivative may comprise(difluorophenyl)thiourea or [(trifluoromethyl)phenyl]thiourea.

A two-part, dual-curing dental composition is provided that comprisesboth chemical initiation to activate polymerization, as well asinitiation upon exposure to an external energy source. For example, thedental composition may further comprise a photoinitiator or aphotopolymerizable component, rendering the dental composition curableupon the application of a light source. A self-adhesive dentalcomposition may further comprise a polymerizable acidic monomer capableof etching hard dental structures, such as enamel or dentin.

A two-part dual-curing, self-adhesive dental composition is providedthat has a first part comprising a polymerizable monomer having anacidic functional group, optionally, a polymerizable monomer having noacidic functional group, and a hydroperoxide compound. A second partcomprises a polymerizable monomer having no acidic functional group, acomposition comprising fluoro or trifluoromethyl substitutedphenylthiourea, a photoinitiator system, and an acetylacetonate salt. Ina further embodiment, a two-part system dual-curing, self-adhesivedental cement is provided that comprises a catalyst paste comprising, ahydroperoxide compound, a polymerizable acidic monomer, a polymerizablenon-acidic monomer, a filler and a stabilizer, and a base paste thatcomprises a composition comprising fluoro or trifluoromethyl substitutedphenylthiourea, a polymerizable non-acidic monomer, an acetylacetonatesalt, a photoinitiator, a filler, and a stabilizer.

Advantageously, a dental composition formed as a two-part systemcomprising a catalyst paste and a base paste may be stored in a dualchamber syringe. The pastes are stored in separate compartments, and maybe mixed, e.g., in approximately a 1:1 volume ratio, immediately priorto application; optionally, the pastes may be dispensed through anauto-mixing tip attached to the syringe.

Dual-curing, self-adhesive dental cement compositions comprising theredox initiator, a hydroperoxide compound and a composition comprisingfluoro or trifluoromethyl substituted phenylthiourea, demonstrateimproved properties when stored for an extended time at room temperaturecompared to dental compositions that include known benzoylperoxide/tertiary amine initiator systems. Self-adhesive dentalcompositions are provided that are stable upon long term storage at hightemperatures. For example, dual-curing self-adhesive dental compositionsare provided herein that may be stored at approximately 50° C. for atleast 16 weeks, maintaining acceptable working time, setting time, andcolor stability, and optimized flexural strength, flexural modulus andbonding strength.

DETAILED DESCRIPTION

Two-part, self-curing, or dual-curing, dental compositions are providedfor use in applications such as, dental provisional materials, resincomposites and resin cements. The dental compositions may be suitablefor self-adhesive cements and conventional resin cements that require aseparate adhesive system.

Self-curing dental compositions may comprise a first part comprising ahydroperoxide compound as an oxidizing agent and a polymerizablemonomer, and a second part that comprises a reducing agent comprisingfluoro or trifluoromethyl substituted phenylthiourea, apolymerizable-monomer, and an acetylacetonate salt. In a furtherembodiment, the two-part system is dual-curing, further comprising, forexample, a photoinitiator system.

A dual-curing, self-adhesive dental cement is provided that etches,primes and adheres in one step. The composition may comprise a firstpart comprising a hydroperoxide compound, a polymerizable acidic monomerand, optionally, a polymerizable non-acidic monomer, and a second partthat comprises a fluoro or trifluoromethyl substituted phenylthiourea, apolymerizable non-acidic monomer, and an acetylacetonate salt.

A two-part, dual-curable self-adhesive composition may be provided as apaste/paste system, wherein a catalyst paste comprises a hydroperoxidecompound, a polymerizable monomer comprising an acidic group, a fillerand a stabilizer, and a base paste that comprises a fluoro ortrifluoromethyl substituted phenylthiourea containing compound, apolymerizable monomer without an acidic group, an acetylacetonate salt,a filler, a photoinitiator, and a stabilizer.

A self-curing initiator system suitable for use herein that chemicallyinitiates polymerization of polymerizable monomers, compriseshydroperoxide as an oxidizing agent. The oxidizing agent may compriseone or more hydroperoxide-containing compounds such as, cumenehydroperoxide, t-butyl hydroperoxide, p-diisopropylbenzenehydroperoxide, t-amyl hydroperoxide, pinane hydroperoxide, p-menthanehydroperoxide, or 1,1,3,3-tetramethylbutyl hydroperoxide, orcombinations thereof. The total concentration of hydroperoxide in thetwo-part dental composition is sufficient to initiate radicalpolymerization when mixing the first part and the second part; in oneembodiment, the concentration is sufficient to maintain an acceptableworking time to apply and/or manipulate the dental composition beforecuring and bonding occurs. Concentrations of hydroperoxide compoundsuitable for use herein may be in a range such as, 0.1% by weight to 5%by weight, or 0.3% by weight to 5% by weight, or 0.5% by weight to 4% byweight, or 0.5% by weight to 3% by weight, based on the total weight ofthe catalyst part, including components such as fillers, resins, and thelike.

Reducing agents suitable for use herein include compositions comprisinga fluoro or trifluoromethyl substituted phenylthiourea; includingcombinations thereof. As used herein, fluoro or trifluoromethylsubstituted phenylthiourea, refers to a composition comprising athiourea derivative comprising phenyl, wherein phenyl comprises one ormore substituents selected from fluorine and trifluoromethyl. In someembodiments, a reducing agent may comprise (difluorophenyl)thiourea,which by way of example includes, but is not limited to,(2,3-difluorophenyl)thiourea, or a reducing agent may comprise[(trifluoromethyl)phenyl]thiourea, which includes, but is not limitedto, [3-(trifluoromethyl)phenyl]thiourea and[4-(trifluoromethyl)phenyl]thiourea. Reducing agents may comprisecombinations of more than one fluoro or trifluoromethyl substitutedphenylthiourea, such as, combinations of more than one(difluorophenyl)thiourea, or more than one[(trifluoromethyl)phenyl]thiourea, or combinations of(difluorophenyl)thiourea and [(trifluoromethyl)phenyl]thiourea. Inaddition to fluoro or trifluoromethyl substituted phenylthiourea,reducing agents may comprise other thiourea reducing agents, such aslinear and cyclic substituted thiourea reducing agents. Theconcentration of fluoro or trifluoromethyl substituted phenylthioureamay be in a range such as, 0.1% by weight to 5% by weight, or 0.2% byweight to 3% by weight, or 0.2% by weight to 2% by weight, or 0.2% byweight to 1.5% by weight, or 0.1% by weight to 1% by weight, based onthe total weight of the base part including components such as fillers,resins, and the like.

Self-curing, self-adhesive dental compositions may contain apolymerizable acidic monomer. As used herein, acidic monomers refers tomonomers having an acidic functional group suitable for etching a harddental surface, including but not limited to a phosphate group,phosphonic acid group, carboxylic acid group or sulfonic acid group, orcombinations thereof. In one embodiment, the catalyst part may comprisea polymerizable, acrylate- or methacrylate-containing monomer comprisingan acidic group. Methacryloyloxydecyl phosphate (MDP),glyceryldimethacrylate phosphate (GDM-P), hydroxyethylmethacrylatephosphate (HEMA-P), phenyl methacryloxyethyl phosphate (phenyl-P),dipentaerythritol pentaacrylate phosphate (PENTA-P),bis(hydroxyethylmethacrylate) phosphate (Bis(HEMA)-P),4-methacryloxyethyl trimellitic acid (4-MET), 10-methacryloxydecylmalonic acid (MAC-10), pyromellitic dianhydride glycerol dimethacrylateadduct (PMGDM), pyromellitic dimethacrylate (PMDM) or pyromelliticdimethacrylate mixture of isomers (PMDM), or combinations of more thanone, thereof, may be suitable for use in self-curing and dual-curingdental compositions described herein. Concentrations of polymerizablemonomers having acidic functional groups may be in the range of 1% byweight to 20% by weight, or in the range of 1% by weight to 10% byweight, based on the total weight of the catalyst part.

Dental compositions may comprise one or more polymerizable non-acidicmonomers. As used herein, non-acidic monomer refers to a monomer withoutan acidic functional group, such as an acid phosphate, phosphonic acid,carboxylic acid or sulfonic acid group. Both catalyst and base parts maycontain a non-acidic monomer, and the non-acidic monomer contained in acatalyst part may be the same or different as non-acidic monomercontained in a base part. Polymerizable non-acid monomers may comprisehydroxyethyl methacrylate (HEMA), hydroxypropyl methacrylate (HPMA),hydroxybutyl methacrylate (HBMA), glycerol monomethacrylate (GMMA),glycerol dimethacrylate (GDMA), pentaerythritol trimethacrylate (PETMA),bisphenol A glycidyl methacrylate (BisGMA), ethyleneglycoldi(meth)acrylate (EGDMA), diethyleneglycol dimethacrylate (DEGDMA),triethyleneglycol dimethacrylate (TEGDMA), tetraethyleneglycoldimethacrylate [(PEG)4DMA], ethoxylated bis phenol A mimethacrylate(EBPADMA), 1,6-hexanediol dimethacrylate (HDDMA), 1,10-decanedioldimethacrylate (D3MA), neopentyl glycol dimethacrylate (NPDMA), urethanedimethacrylate (UDMA), or trimethylolpropane trimethacrylate (TMPTMA),or combinations of one or more thereof. The concentration ofpolymerizable non-acidic monomer in the catalyst part may be the same ordifferent as the base part, and the concentration may be, for example,in the range of 5% by weight to 70% by weight, or 10% by weight to 40%by weight, based on the total weight of the individual part.

Catalyst parts and base parts may each comprise a filler, for example,to impart desired mechanical properties to the dental composition. Afiller may comprise, for example, fumed silica, colloidal silica, orprecipitated silica, silicate glass, aluminosilicate glass,aluminoborosilicate glass, fluoroaluminosilicate glass,bariumaluminosilicate glass, bariumaluminoborosilicate glass,strontiumaluminosilicate glass, bariumfluoroaluminosilicate glass,strontiumfluoroaluminosilicate glass, strontiumzincfluoroaluminosilicateglass, zincaluminosilicate glass, ytterbium fluoride, yttrium fluoride,strontium fluoride, barium fluoride, or combinations of one or morefillers, thereof. Concentration of filler may be, for example, in arange of 20% by weight to 80% by weight, based on the total weight ofthe catalyst or base paste, or in a range of 50% by weight to 75% byweight, or in the range of 40% by weight to 75% by weight, based on thetotal weight of the catalyst or base paste. Optionally, the surface of afiller may be treated or coated by a coupling agent, such as3-(trimethoxysilyl)propyl methacrylate, to promote the interfacialinteraction of the filler and resin matrix.

Acetylacetonate salt that works with a reducing agent comprising afluoro or trifluoromethyl substituted phenylthiourea and an oxidizingagent comprising hydroperoxide to generate radicals that initiateradical polymerization, may be incorporated in the base part. Forexample, a base part may comprise an acetylacetonate salt, such as,vanadyl acetylacetonate (VO(AcAc)₂) or copper (II) acetylacetonate(Cu(AcAc)₂), in a concentration in the range of 0.00005% by weight to0.05% by weight, or 0.0005% by weight to 0.0050% by weight, or 0.001% byweight to 0.003% by weight, based on the total weight of the base part.

Curable dental compositions that self-cure upon mixing through chemicalinitiation, may also be dual-curing. For example, dental compositionsmay further comprise an initiator system for curing dental compositionsupon the application of an external energy source, including heat orlight, such as a blue light source. Known photoinitiator systems forcuring dental composites by known technologies in the dental industrymay be suitable for use herein. In some embodiments, a photoinitiatormay comprise benzoin, acetophonone, diketone, acylphosphine oxide,ketal, diaryliodonium salt, triarylsulfonium salt, or combinations ofone or more thereof.

The catalyst part, the base part or both parts, may comprise known ainhibitor and/or stabilizer, such as a UV stabilizer, that inhibitspolymerization or that improves color stability. Compositions mayinclude but are not limited to 2,6-di-(tert-butyl)-4-methylphenol (BHT),4-methoxyphenol (MEHQ), 2-hydroxy-4-methoxybenzophenone (UV-9), orcombinations thereof.

In a two-part system, such as a catalyst paste and base paste system,components may be contained separately, such as in separate compartmentsof a dual-chamber syringe. Upon mixing the two parts, oxidizing andreducing agents react to form radicals that polymerize the dentalcomposition. In one embodiment, a catalyst paste and a base paste aredispensed through an automixing tip of a dual-chamber syringe, and mixedin a ratio of approximately 1:1 by volume.

Advantageously, dental compositions provided herein, comprising ahydroperoxide and a fluoro or trifluoromethyl substituted phenylthioureasuch as (difluorophenyl)thiourea or [(trifluoromethyl)phenyl]thiourea,redox initiator system, remain curable after long-term storage at hightemperatures. Dental compositions exhibit good color stability, workingtime, setting time, bonding strength, and flexural strength and modulusafter storing for at least 12 weeks, or at least 16 weeks, at 50° C.,when tested according to the methods described herein. Compositionsprovided herein have a working time greater than 90 seconds and asetting time of less than 10 minutes after 12 weeks, or after 16 weeks,or after 19 weeks, at 50° C., when tested according to the methodsdescribed herein.

Test Method

Shear Bond Strength

Shear bond strength to molar dentin was tested in self-cure mode,light-cure mode, and dual-cure mode, as indicated herein. Samplepreparation and testing was conducted substantially according to themethod provided in ISO 29022 (Notched-edge shear bond strength test))(2013). Curing condition were as follows. Self-curing samples were curedfor 15 minutes at 37° C.; light cured samples were cured for 20 seconds.Samples were dual-cured by first curing for 5 minutes at 37° C.,followed by light curing for 20 seconds with light intensity of about600 mW/cm².

Working/Setting Time, Flexural Strength, Flexural Modulus, and ColorStability

Samples were prepared and tested according to the test methods providedin ISO4049, Fourth edition, 2009 Oct. 1, for working and setting times,flexural strength, flexural modulus, and color stability (delta E).

Slump

Slump was determined according to the modified method provided in ISO4823 (1992) as modified for elastomeric impression materials.

Stability Testing-Accelerated Aging

Dual-chamber syringes were filled with catalyst and base pastes, andstored in an oven at 50° C. Samples were tested at an initial time, andremoved from the oven for testing at proposed time until samples weredepleted.

EXAMPLES

Abbreviations for components used to prepare compositions, are asfollows:

BisGMA—bisphenol A glycidyl methacrylate

HEMA—hydroxyethyl methacrylate

UDMA—di-2-methacryloxyethyl 2,2,4-trimethylhexamethylene-dicarbamate

EBPADMA—ethoxylated bisphenol A dimethacrylate with 2 to 4 units ofethoxylation

TEGDMA—triethyleneglycol dimethacrylate

GDMA—glycerol dimethacrylate, mixture of isomers

TMPTMA—trimethylolpropane trimethacrylate

MDP—10-methacryloyloxydecyl dihydrogen phosphate

CQ—camphorquinone

EDMAB—ethyl-4-dimethylamino benzoate

BTPPO—Bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide

CHP—cumene hydroperoxide

BHT—butylated hydroxytoluene

2FPhTU—(2,3-difluorophenyl)thiourea

3-FPhTU—[3-(trifluoromethyl)phenyl]thiourea

4-FPhTU—[4-(trifluoromethyl)phenyl]thiourea

Cu(AcAc)₂—copper(II) acetylacetonate

MPTMS—3-(trimethoxysilyl)propyl methacrylate

OX-50-Sil—fumed silica OX-50 silinated with MPTMS

R202—fumed silica treated with a polydimethylsiloxane

FAS-sil—Fluoroaluminosilicate glass silinated with MPTMS

BG-sil—Bariumfluoroaluminosilicate glass silinated with MPTMS

YbF₃—ytterbium(III) fluoride powder

WS—working time (in minutes (′), seconds (″))

ST—setting time (in minutes (′), seconds (″))

FS—flexural strength

FM—flexural modulus

SBS—shear bond strength

Delta E (ΔF)—color difference between the aging and fresh samples

Base Paste and Catalyst Pastes Compositions

Two-part catalyst paste/base paste dental compositions were formulatedfor self-adhesive dental cement applications. Compositions comprisingacidic monomers, non-acidic monomers, fillers, inhibitor/stabilizers,hydroperoxide, photoinitiator system, thioureas, and acetylacetonatesalt, used to make the catalyst and three base pastes, are provided inTable 1. The weight percent (% wt) of each component is based on thetotal weight of the individual catalyst paste or base paste composition.A reducing agent used for each base paste was selected from (2,3-difluorophenyl)thiourea (2FPhTU), [3-(trifluoromethyl)phenyl]-thiourea(3-FPhTU), and [4-(trifluoromethyl)-phenyl]thiourea (4-FPhTU), asindicated in the table below.

TABLE 1 Catalyst Paste and Base Pastes Formulations. Catalyst Base 1Base 2 Base 3 component (% wt) (% wt) (% wt) (% wt) BisGMA 9.954% 7.078%7.078% 7.078% GDMA 4.835% — — — TMPTMA 4.266% — — — HEMA 5.688% 2.949%2.949% 2.949% H₂O 0.853% — — — MDP 2.844% — — — UDMA — 8.847% 8.847%8.847% EBPADMA — 8.847% 8.847% 8.847% TEGDMA — 1.475% 1.475% 1.475% CQ —0.059% 0.059% 0.059% EDMAB — 0.177% 0.177% 0.177% BTPPO — 0.059% 0.059%0.059% BHT 0.060% 0.006% 0.006% 0.006% CHP 1.500% — — — F2PhTU — 0.501%— — 3-FPhTU — — 0.501% — 4-FPhTU — — — 0.501% Cu(AcAc)₂ — 0.002% 0.002%0.003% BG-Sil 60.000%  — — — FAS-Sil 60.000%  60.000%  60.000% OX-50-Sil 5.000% 4.000% 4.000% 4.000% R202 — 1.000% 1.000% 1.000% YbF₃5.000% 5.000% 5.000% 5.000% 100.000%  100.000%  100.000%  100.000% 

Example 1

A two-part dual curing, self-adhesive dental composition was preparedand tested after aging.

Catalyst and Base 1 pastes were separately prepared that containedcomponents listed in Table 1. Base 1 comprised a thiourea,(2,3-difluorophenyl)thiourea (2FPhTU). Catalyst and base pastes wereseparately filled into a 1:1 ratio dual-barrel syringe and aged at 50°C. for up to 19 weeks. For testing, the two pastes were mixed through anautomixing tip by pushing a plunger in the syringe.

Sample compositions were aged at 50° C. for up to 19 weeks, or untilsample compositions were depleted. Measurements were obtained forworking times (WT) and setting times (ST), reported in minutes (′) andseconds (″). Shear bond strength (SBS) to molar dentin (measured forself-cure mode, light-cure mode and dual-cure mode), values are reportedas MPa. Flexural strength (FS), reported as MPa, and flexural modulus(FM), reported as GPa, were measured for self-cure modes. Results andstandard deviations (s.d.), are provided in Table 2. Slump (reported incm) and color change (A E) of the compositions, were measured forfreshly prepared and aged samples, as reported in Table 2.

TABLE 2 Properties of Catalyst and Base 1 Composition. SBS FS FM MPa MPaGPa WT ST (s.d.) (s.d.) (s.d.) Ex. 1 min./sec. min./sec. Self- Light-Dual- Self- Self- Slump (50° C.) (s.d.) (s.d.) Cure Cure Cure Cure CureΔE (cm) Initial 2′ (23″) 3′51″ (31″) 11.6 (3.2) 9.5 (8.2) 7.6 (3)   73.4(5.9) 5.38 (0.51) 0.00 2.73 2 wks 2′11″ (8″) 3′20″ (13″) 6.2 (1.4) — — —— — — 4 wks 2′32″ (15″) 3′34″ (24″) 7.6 (3) — — — — — — 6 wks 4′19″(47″) 5′12″ (47″) 5.3 (1.8) — — — — — — 8 wks 4′18″ (22″) 5′17″ (21″)4.1 (1.6) — — — — — — 10 wks 3′7″ (12″) 4′7″ (15″) 3.7 (2) 5.2 (1.3) 7.6(5.7) 113.9 (8.8)  7.21 (0.49) 1.52 — 12 wks 7′35″ (58″) 7′55″ (51″) 7.4(2.4) 7.3 (2)   9.4 (4.8) 101.4 (10.0) 5.92 (0.76) 2.40 2.7  14 wks4′43″ (4″) 5′5″ (7″) 5.5 (2.1) — — — — 2.95 — 16 wks 6′7″ (14″) 6′33″(15″) 2.6 (1.6) — — — — — — 17 wks 7′30″ (14″) 7′55″ (7″) 1.6 (0.2) — —— — — — 18 wks 3′27″ (21″) 4′3″ (21″) 4.4 (2.5) — — — — — — 19 wks 4′50″5′10″ — — — — — — —

Sample compositions of Example 1 exhibited good stability at 50° C.throughout the testing period which continued until compositions weredepleted. For example, working time (WT) and setting time (ST) were4′50″ and 5′10″ after aging for 19 weeks, compared to initial WT 2′ andST 3′51″, respectively. The change in color (ΔE) was less than 3 afteraging for 14 weeks. After aging for 12 weeks, shear bond strength was7.4 MPa for self-cure and 7.3 MPa for light-cure, SBS of dual-cure was9.4 MPa. Flexural strength (FS) increased after 12 weeks, compared toinitial time. There was almost no change in slump.

Example 2

A two-part dual curing, self-adhesive dental composition was preparedand tested after aging.

Catalyst and Base 2 pastes were prepared comprising the componentslisted in Table 1. Base 2 comprised a thiourea,[3-(trifluoromethyl)phenyl]thiourea (3-FPhTU). Catalyst and Base 2pastes were separately filled into a 1:1 ratio dual-barrel syringe andaged at 50° C. for up to 16 weeks. For testing, the two pastes weremixed through an automixing tip by pushing a plunger in the syringe.

Measurements were obtained for working times (WT) and setting times(ST), reported in minutes (′) and seconds (″). Shear bond strength (SBS)to molar dentin values (measured for self-cure mode, light-cure mode anddual-cure mode) are reported as MPa. Flexural strength, reported as MPa,and flexural modulus (FM), reported as GPa, were measured for self-curemodes. Results and standard deviations (s.d.), are provided in Table 3.Slump, reported in (cm), and color change (ΔE) of the compositions, arereported in Table 3.

TABLE 3 Properties of Catalyst and Base 2 Composition. SBS FS PM MPa MPaGPa WT ST (s.d.) (s.d.) (s.d.) Ex. 2 min./sec. min./sec. Self- Light-Dual- Self- Self- Slump (50° C.) (s.d.) (s.d.) Cure Cure Cure Cure CureΔE (cm) Initial 1′55″ (17″) 3′14″ (14″) 5.8 (2) 6.6 (5.6) 7.8 (3.2) 98.3(8.1)  7.28 (0.33) — 3.03 2 wks 2′53″ (14″) 3′54″ (22″) 3.6 (0.9) — — —— — — 4 wks 3′57″ (23″) 5′53″ (15″) 9.2 (6.6) — — — — — — 6 wks 2′57″(19″) 4′27″ (23″) 3.8 (1.9) — — — — — 2.93 8 wks 3′30″ (22″) 4′17″ (40″)3.8 (2) — — — — — — 10 wks 3′19″ (10″) 4′27″ (25″) 6.4 (1.1) 5.6 (2)  4.7 (2.2) 98.7 (13.8) 7.12 (0.49) 1.14 — 12 wks 4′42″ (13″)  5′8″ (20″)5.1 (3.1) 8.8 (6.5) 8.3 (3.7) 92.5 (23.8) 6.81 (0.54) 1.63 2.65 14 wks9′25″ (15″) 9′50″ (17″) 4.6 (2.2) — — — — — — 16 wks 5′53″ (21″) 6′13″(21″) 4.5 (1.7) — — — — — —

Sample compositions of Example 2 also showed good stability at 50° C.throughout the testing period. For example, working time (WT) andsetting time (ST) were 5′53″ and 6′13″, respectively, after 16 weeks at50° C. Color difference measurements (ΔE) were less than 2 after agingfor 12 weeks. After aging for 12 weeks, shear bond strength (SBS)remained about the same and for self-cure SBS was 5.1 MPa, 8.8 MPa forlight-cure and 8.3 MPa for dual-cure.

Example 3

A two-part dual curing, self-adhesive dental composition was preparedand tested after aging.

A catalyst paste was provided having the same formulation as describedin Example 1, according to the composition of Table 1. Base 3 paste wasprepared using [4-(trifluoro-methyl)phenyl]thiourea (4-FPhTU) as thethiourea according to the composition of Table 1. The catalyst and Base3 pastes were separately filled into a 1:1 ratio dual-barrel syringe,and aged at 50° C. for up to 16 weeks. For testing, the two pastes weremixed through an automixing tip by pushing a plunger in the syringe.

Measurements were obtained for working times (WT) and setting times(ST), reported in minutes (′) and seconds (″). Shear bond strength (SBS)to molar dentin values (measured for self-cure mode, light-cure mode anddual-cure mode) are reported as MPa. Flexural strength, reported as MPa,and flexural modulus (FM), reported as GPa, were measured for self-curemodes. Results and standard deviations (s.d.), are provided in Table 4.Color change (delta E) values of the compositions are reported in Table4.

TABLE 4 Properties of Catalyst and Base 3 Combinations. SBS FS FM MPaMPa GPa WT ST (s.d.) (s.d.) (s.d.) EX. 3 min./sec. min./sec. Self-Light- Dual- Self- Self- (50° C.) (s.d.) (s.d.) Cure Cure Cure Cure cureΔE Initial 1′58″ (11″) 3′34″ (8″) 5.6 (27)  9.58 (2.82) 9.63 (5.96) 97.6(15.9) 7.36 (0.35) — 2 wks 1′53″ (14″) 3′28″ (13″) 5.80 (2.66) 6.60(2.89) 9.10 (2.69) 108.3 (17.7) 7.56 (0.31) — 4 wks 1′54″ (13″) 3′18″(15″) 4.78 (1.28) 6.13 (1.61) 8.74 (4.68) 99.6 (16.7) 7.79 (0.46) — 6wks 1′58″ (14″) 3′43″ (24″) 5.92 (3.60) 9.47 (4.18) 8.11 (2.83) 107.7(13.5) 7.72 (0.36) 1.32 8 wks 2′27″ (23″) 4′14″ (31″) 5.12 (0.82) 6.19(2.87) 6.30 (2.65) 106.9 (25.9) 7.55 (0.16) — 10 wks 3′10″ (17″) 5′ (7″)3.89 (1.07) 6.28 (2.67) 4.65 (1.08) 100.6 (13.4) 7.72 (0.43) — 12 wks 3′3″ (22″) 5′2″ (30″) 2.92 (0.75) 4.97 (2.65) 7.62 (2.07) 114.1 (11.8)7.62 (0.40) 0.60 14 wks 2′12″ (13′) 4′26″ (17″) 5.41 (2.95) 7.69 (3.29)6.29 (2.46) — — — 16 wks — — 2.32 (1.93) 8.04 (4.16) 8.79 (1.76) 76.9(13.3) 5.43 (0.28) 0.97

Sample compositions of Example 3 showed good stability at 50° C.throughout the testing period, which continued until compositions weredepleted. There were no significant changes between the initial test andaged samples, for example, for working time (WT) and setting time (ST)and color difference (ΔE) measurements were less than 2 after aging for12 and 16 weeks.

We claim:
 1. A two-part curable dental composition comprising a) a firstpart comprising a polymerizable monomer having an acidic functionalgroup, a first polymerizable monomer having no acidic functional group,and a hydroperoxide compound; and b) a second part comprising a secondpolymerizable monomer having no acidic functional group, a compositioncomprising a fluoro or trifluoromethyl substituted phenylthiourea, andan acetylacetonate compound, wherein the first part, the second part, orboth, optionally comprise a filler; and wherein the dental composition,stored for at least 16 weeks at 50° C.: (i) is curable upon mixing thefirst paste and the second paste, (ii) has a working time and a settingtime of at least 90 seconds and less than 10 minutes, and (iii) has adelta E of less than
 3. 2. The two-part dental composition of claim 1,where the first part is a paste and the second part is a paste.
 3. Thetwo-part dental composition of claim 1, wherein the polymerizablemonomer having an acidic functional group comprises methacryloyloxydecylphosphate, glyceryldimethacrylate phosphate, hydroxyethylmethacrylatephosphate, phenyl methacryloxyethyl phosphate (phenyl-P),dipentaerythritol pentaacrylate phosphate, orbis(hydroxyethylmethacrylate) phosphate, or a combination thereof. 4.The two-part dental composition of claim 1, wherein the polymerizablemonomer having an acidic functional group comprises 4-methacryloxyethyltrimellitic acid, or 10-methacryloxydecyl malonic acid, or a combinationthereof.
 5. The two-part dental composition of claim 1, wherein thepolymerizable monomer having an acidic functional group has aconcentration of 1% by weight to 20% by weight of the first part.
 6. Thetwo-part dental composition of claim 1, wherein the hydroperoxidecompound comprises cumene hydroperoxide, t-butyl hydroperoxide,p-diisopropylbenzene hydroperoxide, t-amyl hydroperoxide, pinanehydroperoxide, p-menthane hydroperoxide, or 1,1,3,3-tetramethylbutylhydroperoxide, or a combination thereof.
 7. The two-part dentalcomposition of claim 1, wherein the hydroperoxide compound has aconcentration of 0.1% by weight to 5% by weight of the first part. 8.The two-part dental composition of claim 1, wherein the compositioncomprising fluoro or trifluoromethyl substituted phenylthioureacomprises (2,3-difluorophenyl)-thiourea,[3-(trifluoromethyl)-phenyl]thiourea, or [4-(trifluoromethyl)phenyl]thiourea, or a combination thereof.
 9. The two-part dentalcomposition of claim 1, wherein the second part comprises vanadylacetylacetonate, vanadium(III) acetylacetonate or copper(II)acetylacetonate, or a combination thereof.
 10. The two-part dentalcomposition of claim 1, wherein the first part comprises a filler, andthe second part comprises a second filler that is different from thefirst filler.
 11. The two-part dental composition of claim 1, whereinthe composition is a dual-curing composition and the second part furthercomprises a photoinitiator.
 12. The two-part dental composition of claim1, wherein the composition further comprises a stabilizer.
 13. A curabledental composition comprising a) a first paste comprising: at least onepolymerizable monomer having an acidic functional group, at least onepolymerizable monomer having no acidic functional group, and ahydroperoxide compound; and b) a second paste comprising at least onepolymerizable monomer having no acidic functional group, a compositioncomprising (difluorophenyl)thiourea or[(trifluoromethyl)phenyl]thiourea, a photoinitiator, and anacetylacetonate compound, wherein the dental composition furthercomprises a filler; and wherein the dental composition, stored for atleast 16 weeks at 50° C.: (i) is curable upon mixing the first paste andthe second paste, (ii) has a working time and a setting time of at least90 seconds and less than 10 minutes, and (iii) has a delta E of lessthan
 3. 14. The curable dental composition of claim 13, comprising(2,3-difluorophenyl)-thiourea, [3-(trifluoromethyl)phenyl]thiourea, or[4-(trifluoromethyl)phenyl]-thiourea, or combinations thereof.
 15. Thecurable dental composition of claim 13, wherein the at least onepolymerizable monomer having an acidic functional group comprises aphosphate group, a carboxylic acid group, or sulfonic acid group.